Field of the Invention
The present invention relates to uninterrupted lithium battery power supply systems and methods of using said system, in one embodiment, a battery management system is configured to monitor the state of charge of a battery unit. In another embodiment, a system and method for automatically balancing a battery unit is provided. In particular, a battery balancing system may activate a discharging circuit that draws a constant discharging current from a battery unit when the voltage of a battery within the battery unit exceeds a predetermined threshold.
Background
Lithium ion batteries require special controls in back-up power systems, —as they require monitoring of their state of charge to ensure that they are not operated below a threshold voltage value and/or are not over charged. Lithium batteries can be irreversibly damaged if operated below a threshold voltage value. Lithium batteries may lose their ability to be fully charged if they are operated below a threshold voltage for too long. A plurality of lithium batteries would be required to generate the voltage needed for most uninterrupted power supply systems and therefore a plurality of lithium batteries may need to be connected in series. When a plurality of batteries are coupled together, it is important to keep the level of charge of each battery within a range of the other batteries to prevent damage and to get maximum capacity.
As shown in FIG. 1, lithium batteries have a non-linear discharge profile, with a relatively flat discharge region up to about 80% discharged. Therefore, a small change in voltage can mean a large difference in the state of charge, unlike a lead acid battery that has a relatively linear drop in voltage as the battery is discharged. The state of charge of a lead acid battery, and therefore the amount of power remaining, is more easily monitored by a UPS system by simply monitoring the voltage of the lead acid battery. The amount of power remaining in a lithium battery system is more difficult to monitor and predict however by simply measuring voltage. It would therefore be more difficult to determine the available power remaining in a lithium battery unit by simply measuring the voltage.
Current battery management systems obtain data about individual batteries in a battery unit. The systems reserve addresses for communication with battery unit sensors and/or battery units. When sensors transmit data about battery units to the management system, the sensors include the address of the battery unit. Such a system may require significant amounts or resources and complex arrangements for connecting the components of the system.
Current charging systems are configured to charge a battery pack to a predetermined voltage. However, the individual battery may not be charged to the same level, and the discrepancy between the batteries state of charge levels can cause capacity to be limited. The battery pack capacity is limited to the capacity of the lowest battery unit. Additionally, when some battery units have lower state-of-charge levels, as the battery discharges, those units may discharge to a level resulting in permanent loss of charging capacity.